Smart start systems are being utilized, which enable starting of motors installed in vehicles without the use of a mechanical key. Smart start systems are constituted by a portable device possessed by a user, and an on-board device that detects the position of the portable device when an engine start switch is depressed, or when the user grasps the door handle, and performs motor start processing or vehicle door locking or unlocking processing.
When the user depresses the engine start switch, the on-board device transmits wake-up signals from a plurality of LF transmitting antennas provided inside the vehicle, and activates the portable device. The activated portable device transmits to the vehicle a specified signal indicating its existence. When the on-board device receives the specified signal, it transmits, from the LF transmitting antennas, detection signals for detecting the position of the portable device. The portable device receives the detection signals transmitted from the various LF transmitting antennas, and measures the received signal strengths. The portable device then transmits information regarding the measured received signal strengths to the on-board device. The on-board device receives the information regarding the measured received signal strengths from the portable device, determines whether the portable device is inside the vehicle, and performs processing corresponding to the determination result. For example, if the portable device is positioned inside the vehicle, the on-board device performs motor starting processing.
In Publication JP-A-2010-236346 (P2010-236346A), an on-board device and a portable device are disclosed that can shorten processing time. The on-board device improves communication processing speed by simultaneously transmitting signals, with a phase difference provided, from a plurality of LF transmitting antennas inside the vehicle.
Meanwhile, in a conventional smart start system, when there are a plurality of portable devices, a portable device is activated for each LF transmitting antenna, and transmitting and receiving of information necessary for determining whether the activated portable devices are inside or outside the vehicle is separately performed for each portable device.
FIG. 11 is a timing chart that shows signals transmitted and received in conventional portable device position detection processing. In a vehicle, there are provided first through fifth LF transmitting antennas that transmit detection signals for detecting the position of portable devices, and an on-board device transmits various signals such as detection signals from each LF transmitting antenna, and thereby detects the position of the portable devices. There are six portable devices that constitute the smart start system, and the respective portable devices are labeled the first portable device through the sixth portable device. In FIG. 11, “on-board device” is a timing chart showing the processing execution state of an on-board control unit provided in the on-board device. In FIG. 11, “first LF transmitting antenna” through “fifth LF transmitting antenna” are timing charts showing the timing of transmitting signals from the various LF transmitting antennas, and “first portable device” through “sixth portable device” are timing charts showing the timing of transmitting signals from the first through sixth portable devices.
As shown in FIG. 11, in specified cases, the on-board device transmits a wake-up signal from the first LF transmitting antenna. In FIG. 11, the rectangular portions with downward-left hatching show the timing at which the wake-up signal is transmitted. The wake-up signal is transmitted toward the first through sixth portable devices. Each portable device for which the wake-up signal is successfully received is activated from a sleep state, and transmits to the on-board device an ID signal indicating its own existence. In FIG. 11, the rectangular portions with an x-mark show the timing at which ID signals are transmitted. In the example shown in FIG. 11, the first portable device and the second portable device have successfully received the wake-up signal, and each portable device is transmitting its own ID signal to the on-board device.
The on-board device, which has received the ID signals, separately sends detection signals to each activated portable device. For example, when the first portable device and the second portable device have been activated, the on-board device first sends detection signals to the first portable device from the first through sixth LF transmitting antennas. In FIG. 11, the solid black rectangular portions show the timing at which detection signals for detecting portable device position are transmitted. The first portable device measures the received signal strength of the detection signals, and transmits to the on-board device a response signal that includes the received signal strengths obtained by the measurements. In FIG. 11, the rectangular portions with downward-right hatching show the timing at which response signals are transmitted. The on-board device receives the response signal from the first portable device, and performs position detection for the first portable device. That is, the on-board device performs a determination of whether the first portable device is inside the vehicle or outside the vehicle. If the first on portable device is not inside the vehicle, the on-board device sends detection signals to the activated second portable device from the first through sixth LF transmitting antennas, and in the same manner performs position detection for the second portable device.
If the first portable device and the second portable device activated by the wake-up signal from the first LF transmitting antenna are not inside the vehicle, the on-board device next transmits a wake-up signal from the second LF transmitting antenna, and similarly transmits detection signals to the activated portable devices and, based on response signals from the activated portable devices, performs position detection for each portable device. In the example shown in FIG. 11, the third portable device has been activated through the wake-up signal transmitted from the second LF transmitting antenna, and the on-board device performs position detection for the third portable device.
Thereafter, in the same manner, wake-up signals are transmitted from the third through sixth LF transmitting antennas, detection signals are transmitted to the activated portable devices, and position detection is performed for the activated portable devices. The on-board device repeatedly performs the above processing until a portable device is detected inside the vehicle.